Our overall objective is to understand how specific genes are "turned-on" in the development of an organism. Bacteriophage lambda and phi-80 are being investigated as model systems for study because of their amenability to refined biological and biochemical techniques now available. We are characterizing (a) defects in the developmental stages of mutants with presumed defects in control functions at the transcriptional level; (b) individual RNA transcripts according to their precise location on the genome and (c) the exact start-points of these RNA transcripts. Our studies suggest that for bacteriophage lambda, the "turn-on" of messenger RNA by the gene N product (positive control) occurs by an "anti- termination" mechanism; the gene N-dependent RNA transcript is synthesized by elongation of lambda RNA which is initiated by the bacterial host RNA polymerase. Lambda RNA transcripts synthesized in wild-type host strains and mutant host strains defective in RNA metabolism are being studied in detail. Our results show that the gene N-dependent RNA transcript undergoes specific RNA processing either during or after its synthesis.